Antenna system



y 1939. a. T. ROYDEN I 5 ,53

- ANTENNA SYSTEM Filed April 30, 1935 RECEIVER 9' TRANSMISSION LINE .10

FIG.I

. FIG. 2-

mvzuran: QEORGE 1 oman Patented May 23, 1939 UNiTED ms PATENT UFFICE 22,159,637 "ANTENNA SYSTEM George Royden, tPalo Alto, Calif.,' assignorto Maokay "Radio -& Telegraph..Gon1pany, :San Francisco; Galiii, a. corporation of California Application April 30,

BiGlaims.

This invention .relates "to new and 'useful immovements .in antenna systems.

{The object of theinvention is 'to provide an inexpensive directive antenna for short waves 5 and one in which1the reflection of waves fromthe ends of theantenna wire isiminimized.

The invention is applicable to ,radio receiving and transmitting systems and its :nature will be best understood .from .the following detailed de- 1Q ,scriptionof .afew embodiments thereof and the the attenuation .along the-collector wires; Fi 2 illustrates a practical embodiment in which the taperingof the collector wires is effected bythe joint uselof .morethan .one kind and size of conductor, each having a substantially different at- 25 tenuation characteristic per ,unit of length.

Consider .firstthediagram of Fig. .lin which 11,1, 3,35, 5,5 and I, .1 are antenna collector wires connected to successive points along one .sidetof the transmission line T9, and 2, 2, 4, 4', 5,15 and .78, .8 .the collector wires connected to the corresponding successive points along the other sidecf the transmissioniline. "The collector wires ibranch off in .pairstfrom a common transmission ;line, era-preferably. of equal length, and

.35 make equal angles on either side of the axis of symmetry of the collector system. Points of connection iandZ-canLbemade at'theouterrnost u=po1e carrying the:transmissionxlinei and '4 at the next to the last pole, and so on. The trans- 40 mission line .9is designed for eflicient transfer "of energy from the collector system to a radio .receiver 0 in the manner well known to one skilled in theart.

3 It will be noted that the lines representing the *ificollector wires are drawn with varying thickness, i. e., thick at the .ends connectingto the transmission line, and tapering oifto a thin line at theouter ends. The object-of this method of representation'is to .show that the wires are not of .5 0fluniform. conductivity throughout the length of each, but are .of graduated conductivity according to the thickness ofthe' line. The significance Iofwthisis that theattenuation or los'slper unit Ilengthof line varies in the opposite manner to the thickness of-the'line, i. e., a collector of wire 1935, Serial No. 19,002 (Cl. 250 -33) willhave low attenuation per 'unit lengthat'the transmission line endand relatively high attenuation at theouter end-being graduatedbetween these limits throughout its length. This will be clearupon considering the elfect of resistance on the attenuation 'characteristicbf a wireline.

In transmission line theory it is well known that the "attenuation constant A of a given line may beexpressed in terms of the parameters of the line as follows:

where R=resistance per unitlength of line XL=inductanceper unit'length of line G=leakageconductanceper .unit length of line C=capacitance 0:2 1, .I, being the frequency.

At very high frequencies such as I am "dealing with it is'found in practice thatR is very-much less 'inmagnitude than wL and G is'likewisevery much less in magnitude than -wC. This being the case, it is'permissibletosi;plify greatly the expression for A. Hence:

-R C -m Z veryclosely for high frequencies. Thus it will y be seen the attenuation constant for the purpose of my invention is proportional to the conductor resistance and, therefore, inversely proportional tothe conductance. It will be appreciated that the "resistance. referred to is. the effective resistance in the range of frequenciesconsidere'd.

Assuming uniform attenuation in the collector wires, consider whathappen's when radiant energy is impinging on the collector system in the direction of the arrow II. Energy picked up near the outer ends of the collectors must suffer the attenuation of the wholelength of the collectors before reaching the transmission line whereby it is considerably weakened. Energy 7 picked up by the middle portion of the collectors need traverse only a part of their length andarrives at the transmission line in less weakened condition than that which is picked up near the outer ends. Finally, the energy picked up by the portion adjacent to the transmission line is 001- H lected with practically no weakening at all. Consequently, all portions of the collectors are not equally effective in collecting the radiant energy and delivering it to the transmission line, the portions'adjacent to the transmission line being i most effective and the portions near the outer ends being least efiective.

Assuming now that the attenuation is not uniform, but tapered in accordance with my invention, it will be readily apparent that the attenuation is greatest in the portions where the energy picked up contributes the least tothe sum total. Consequently, the energy received with the tapered attenuation is almost as great as that received with a uniform attenuation, if the uniform attenuation were equal to the portion of the tapered attenuation adjacent to the transmission line. This slight sacrifice in received energy is accompanied by important advantages.

Consider, for example, radiant energy arriving from exactly the opposite direction as indicated by arrow I2. This energy impinging on the collectors can be delivered to the transmission line only by reflection at the outer ends of the collectors on account of its direction. In this case, energy picked up near the outer ends is there reflected and must traverse the entire collector to be delivered to the transmission line. Energy picked up in the middle portion must first travel to the outer end being attenuated in the process and, after being reflected, traverse the entire collector before reaching the transmission line. Similarly, energy picked up adjacent to the transmission line must traverse the collector twice, i. e., make a round trip, before being delivered to the transmission line, Therefore, the radiant energy being received from the direction indicated by arrow l2 can be delivered to the transmission line only via the outer ends of the collectors and the contributions to the sum total for various portions of the collectors is the-inverse of the case where 'radiant energy arrives from direction ll.

Assuming the radiation from direction II to be desired,.and that from direction l2 undesired, it will be seen that even with collectors having uniform attenuation there will be some discrimination between front and back reception by the amount of the attenuation of a collector and to that extent it will be desirable. However, it has not been considered beneficial to use collectors of uniformly high attenuation, but rather as low as practicable. This militates against the desired front to back discrimination so that it will not be very great. On the other hand, by tapering the attenuation along the collectors as described, the front to back discrimination is greatly enhanced. The very high attenuation near the outer ends when tapering is employed acts like a bottle-neck to all the back or undesired radiant energy, but the bottle-neck eifect does not come into play when receiving energy from the front or desired direction. My invention, therefore, pro vides a means for reducing the interfering effect on the receiver of radiation arriving from the back direction and at the same time maintaining practically undiminished the effect on the receiver of radiation arriving from the front.

This discriminating effect is still further enhanced by the use of a plurality of pairs of collectors because energy arriving from the front is picked up by the separate pairs of collectors and is delivered to the transmission line in such a manner that the contribution of each pair of collectors adds substantially in phase with the contribution of every other pair, whereas, the energy arriving from the back is not .only squeezed through the bottle-neck of each pair of collectors leaving a relatively small amount to be delivered to the transmission line but the contributions of the individual pairs add in random phase. It will be appreciated that in phase addition means the arithmetical sum of the terms involved, whereas, random phase addition means the sum of component parts of the terms depending on their relative phases which sum is always less in magnitude compared with in phase addition and may in some cases amount to complete cancellation, i

So far, the behavior of the collector system has been treated only in respect to front and back radiation. This is the most important case because an open-ended antenna system of this general type but not employing my arrangement of tapered collectors is arranged to be most receptive in both directions along the axis of the collector system, i, e., front and back reception. In all other directions, except for a small angle on either side of the axis of the collector system, reception is greatly reduced. Therefore, when reception from the back is practically eliminated, as it is with the tapered collectors, the antenna is receptive in substantially one direction, namely, along the axis of the system to radiation arriving from the front as indicated by arrow I I.

In determining the angle, at which the collector wires should fan out from the transmission line, it should be noted that the portions adjacent to the outer ends are more or less inactive as far as collecting energy is concerned. The angle is usually determined by the electrical length of the collector, being smaller as the electrical length is greater. This assumes the collector to be uniformly active throughout its entire length- It is necessary, therefore, to consider only the active length for this purpose. The net result is that a somewhat wider angle should be employed than would be the case if the collector were uniformly active throughout its length. The angle is not very critical and may be estimated closely enough for practical purposes.

Fig. 2 shows one embodiment in which the attenuation of each collector Wire is tapered in discreet steps rather than gradually, as in Fig. 1. Referring to Fig. 2, I3 is the transmission line for conveying the received energy from the collector system'to the receiver 14. The collector system itself is composed of a plurality of pairs of similar composite collector Wires connected at successive points to the transmission line and spreading out at equal angles, the geometry of the system being several sections each section having uniform attenuation throughout thelength of a section, said attenuation'being substantially different for the different sections and relatively short impedance matching devices for interconnecting successive sections. Furthermore, the section of lowest attenuation is adjacent to the transmission line, the remaining sections being of progressively higher attenuation. In Fig. 2, for example, each collector is composed of two sections, l5, l6 and l1, l8 joined by the impedance matching device l6, IT. .Section l5, I6 is adjacent to the transmissionline and is of low attenuation, while section H I1 is adjacent to the outer end and is of relatively high attenuation. In order to achieve lovv attenuation, the section l5, l6 should be of reasonably low effective resistance per unit length and may be, for example, copper wire of the gauge ordinarily used in antennae. Section l1, [8, on

2,159,637 the other hand, should be of relatively small .eauge wire having a relatively high eifective resistance per unit length and may be, for example,

of stainless steel approximately 20 mils in di-.

ameter. By reference to the simplified formula for theattenuation constant A given above, it maybe shown that the section II, I8 has a high attenuation per unit length compared with section l5, I6.

Theimpedance matching device l6, l! is necessary in this arrangement in order to realize the full benefit of the bottle-neck eifect because a direct connection between the copper wire of sec- II, I8, said wires having widely diiferent surge v impedances, would introduce an abrupt. im-

pedance irregularity at the junction of the wires. Such an impedance irregularity would reflect a considerable part of the energy attempting to pass through the junction. This effect is not harmful where the radiation is arriving in the desired direction, i. e., from the front, because then it would act merely to reduce the energy contribution of the high attenuation section I1, it which is purposely negligibly small. How- 'ever, it may be very harmful and, to whatever extent it exists, it tends to defeat the proper functioning of my invention where the radiation is arriving in. the undesired direction, i. e., from the back. What I aim to do is to force the undesired radiation picked up by the collector to make a round trip to the extreme outer end and back whereby it is reduced to negligible proportions by being subjected twice to the high attenuation of the section l1, l8. Obviously, when there is an abrupt impedance irregularity at the junction of wires a considerable part of the undesired radiation is reflected back over'the low attenuation section I 5, l 6 without having been forced to travel first to the outer end. Under these con-. ditions much of the discrimination between front and back radiation would be lost.

In order to overcome this difficulty I employ the relatively simple impedance matching device I5, I I. It comprises two of the stainless steel Wiiesused in section l1, 18 connected in parallel to the end of the copper wire l6, being spaced at this point so that the surge impedance of the spaced stainless steel wires approximately matches that of the copper wire. After a short run, the

stainless steel wires come together at a point H where they are joined to the outer section [1, l8; This graduates the impedance from a value equal to the surge impedance of the copper wire .to a value equaltto the surge impedance of the stainless steel wire, thus eifecting a substantially reflectlonless junction.

Generally, where it is desired to join two wires, one of which has a substantially different surge impedance than the other, in such a manner that there is negligible reflection, Iconstruct the impedance matching device withthe wire having the higher surge impedance connecting the spaced ends to the wire of lower surge impedance and the joined ends to the wire of higher surge impedance. The impedance matching device is, therefore, an isosceles triangle constructed of the wire having the higher surge impedance and having a relatively short base and small angle at the vertex, the base being of such a length that the spaced wires have a surge impedance equal to that of the wire of lower surge impedance. The base is connected to the wireof lower surge impedance and the vertex to the wire of higher surge impedance. In practice the height of the triangle is equal to a plurality of wave lengths where, the antenna is used for short wave transmission or reception and the base is very short as compared to the wave length used.

In actual practice I make section l5, l6 substantially horizontal and about a quarter wave length above the earths surface and five to ten wave lengths long, the impedance matching device about two wave lengths long and section l1, l8 four to six wave lengths long. In order to determine approximately the best angle at which to run the collectors I find that it is desirable to add about two wave lengths to section l5, IS on account of penetration into the outer sections.

WhatI claim is:

1. A directional antenna system comprising a transmission line, and two antenna wires connected therewith and forming a V, the portions of the wires nearest the line having a lower attenuation constant than the portions farthest from the line.

2. An antenna system comprising a transmission line, and antenna wires connected therewith and forming a plurality of parallel Vs, the portions of the wires nearest the line having a lower attenuation constant than the portions farthest from the line.

3. An antenna system comprising a transmissionline, and antenna wires connected therewith and forming a V, one section of each wire. nearest the line having lower attenuation constant than another section, and impedance matching devices between the two sections of each wire.

4. An antenna system comprising a transmission line, and antenna wires connected therewith and forming a plurality of parallel Vs, one section of each wire nearest the line having lower attenuation constant than another section, and impedance matching devices between. the two sections of each wire- 5. In a transmission system, wires of relatively low and high impedance, and an impedance matching device between said wires consisting of an isosceles triangle of relatively high impedance wire the height of which is great and the base of which is of small length as compared to the wave length at which transmission is elfected.

6. A unidirectional antenna system for radiant action with respect to a desired direction, comprising two substantially linear wires of different resistance per unit length disposed end to end along a line obliquely inclined to said desired direction and coupled to each other at their adjacent ends to constitute a conductor of varying attenuation 'along its length and a transmission line coupled to that end of said conductor which has the lower attenuation. 

